Almost certainly. Asahi linux is getting pretty useable on M1 and M2. They don't support M3 yet, let alone M4, but support will surely come eventually.
I would be shocked if they weren't using a test suite, especially given all the platforms and devices Linux supports. POSIX has a test suite, and there are several Linux test suites [1], [2]. Although, I would think that an architecture port is fairly straightforward. It's reverse-engineering and writing all the device drivers, but devices generally have a well-known interface (and, therefore, presumably tests). The OpenGL drivers are being tested against the official OpenGL test suite.
Of course, there are no guarantees that it runs correctly. Probably doesn't, given that even Apple and Microsoft's software don't run correctly, either. But saying software doesn't run perfectly in all cases is almost tautological.
I wouldn't be so sure - if marcan loses interest (already looks like it), who is going to keep up with supporting the latest Apple chips?
When the M series chips were the hot new thing, there sure was developer interest - but now that a new chip is released every year, it becomes boring drudgery.
Look at support for T2 Macs - it took a decade to get them supported, not because the hardware was so different, but mainly because the hardware was 'boring'.
Fair enough, I suppose I could be overly optimistic. I just figure it's garnered enough interest that even if there's turnover in the team somebody will carry the torch. Especially since Apple seems to be actively tolerant if not even supportive of the project.
The other comments talk about Asahi Linux, which doesn't support the M3 yet. You can also run Linux in a VM on MacOS, and it runs very well.
For some uses you won't get the best performance compared to native Linux. But for a Plex/Kodi server a VM should be great.
(On an x86 Apple laptop I found the power consumption better with a Linux VM on MacOS than with native Linux, so VMs can be quite efficient for some uses. Software builds sometimes run much faster in a Linux VM inside MacOS than natively in MacOS. On the other hand, I found Qemu inside a Linux VM for Android development was extremely slow.)
One of the reasons Asahi doesn't support M3, is that Apple never released a Mac Mini, so they can't do continuous integration. [1] That being said, it seems Apple does re use a lot of the parts on the SoC in each generation, so it's not too different.